During connection of tubes of a blood-collecting bag and a blood-component bag in a blood transfusion system, replacement of a waste liquid bag with a dialysate bag, and other operations in continuous ambulatory peritoneal dialysis (CAPD), it is necessary to connect (join) tubes under a sterilized condition. One of apparatuses for aseptically connecting tubes is disclosed for example in Japanese unexamined patent publication No. H6(1994)-78971. An apparatus disclosed in this publication No. H6(1994)-78971 includes a first clamp and a second clamp which hold at least two flexible tubes in parallel relation, a cutting means for cutting the flexible tubes between the first and second clamps, and a moving means for moving at least one of the first and second clamps so that the end portions to be connected of the flexible tubes cut with the cutting means are brought into close contact with each other. The cutting means includes a wafer for melting and cutting the flexible tubes, a constant-voltage source for heating the wafer, a wafer temperature detecting means, and a wafer heating control means. The wafer heating control means has a signal output section for outputting a pulse width modulation calculated based on output of the wafer-temperature detecting means and is arranged to control the temperature of the wafer according to the pulse width modulation signal.
In this apparatus, the wafer heating control means outputs the pulse width modulation signal calculated based on the output of the wafer-temperature detecting means, thereby controlling the temperature of the wafer. In other words, the control of the wafer temperature is performed through feedback control based on the output of the wafer-temperature detecting means.
Another method of controlling the wafer temperature is disclosed for example in Japanese unexamined patent publication No. S59(1984)-64034. The method disclosed in this publication No. S59(1984)-64034 is a method in which electric power for heating a wafer is controlled through constant power control while referring to a temperature at a start of heating up the wafer.
The apparatus disclosed in the above publication '971, however, may cause unstable temperature measurement according to a contact state of the wafer-temperature detecting means with the wafer. Due to long-term use, plasticizer or the like contained in the tubes is likely to adhere to a surface of the wafer-temperature detecting means. Thus the wafer-temperature detecting means may inaccurately measure the temperature of the wafer. Unstable, inaccurate temperature measurement by the wafer-temperature detecting means would lead to unstable, inaccurate control of the wafer temperature. The temperature measurement would become unstable depending on the contact state of the wafer-temperature detecting means with the wafer as mentioned above. For enabling accurate temperature measurement, an adjustment work is performed in mounting the wafer-temperature detecting means. Such adjustment would take much time.
In the wafer-temperature control method disclosed in the publication '034, on the other hand, the wafer temperature is referred to only at the start of wafer heating-up. Thus, when constant electric power is applied to the wafer, a final temperature of the heated wafer may vary from wafer to wafer. In other words, the wafer temperature could not be controlled stably. This is because the presence/absence and direction of thermal flux to each wafer vary due to a difference in elapsed time from a previous connecting operation and other factors. In successive tube connecting operations, particularly, the final temperature of the heated wafer tends to vary.